1. Field of the Invention
This invention relates to monitoring the cleaning, rinsing and drying processes during the manufacture of ICs, MEMS and other micro-devices and more specifically to optimizing the processes to conserve the clean, rinse and dry solutions and energy using an electro-chemical residue sensor (ECRS) for micro-features including surfaces or void micro features.
2. Description of the Related Art
A major challenge in manufacturing of the micro and nano devices is the cleaning and drying of very small void features, particularly those with large aspect ratios. These micro features are fabricated in various processing steps and can be very small voids such as gaps, holes, vias or trenches that are intentionally etched. The micro features can also be pores in a deposited dielectric material. Cleaning and drying occur repeatedly during the processing chain and are responsible for a significant part of the total processing time and for the consumption of much of the water, chemicals and energy.
In semiconductor manufacturing, trenches and vias are fabricated both in the device level and in the interconnect level. Most of these features have high aspect ratios with submicron openings that are oriented perpendicular to the fluid-solid interface of the device to the cleaning fluid and because of their high aspect ratio and very small width are very difficult to clean and dry. In Integrated Circuits, MEMS and other micro device manufacturing, well controlled cleaning and drying are essential to avoid deformation of layers and improper adhesion of moving parts. Improper cleaning and drying would have a significant effect on manufacturing yield and device performance and reliability in both semiconductor and MEMS fabrication. Over-cleaning, over-rinsing or over-drying results in excessive use of chemicals, water and energy and also increases cycle time and potentially causes yield loss. Therefore, there is a strong economic and environmental incentive to use a process that is “just good enough”.
The fine structures left behind after processes such as etching, deposition, and patterning, need to be cleaned and the reaction by-products need to be removed often down to trace levels. This usually involves three steps: 1) application of a cleaning solution; 2) rinsing and/or purging using ultra pure water or other rinsing solutions; and 3) drying by removing and purging the traces of any solvents used during rinsing. Due to the undesirable surface tension associated with aqueous chemicals and non-wetting nature of most future dielectrics, industry is pursing the development of processes based on supercritical fluids such as supercritical carbon dioxide for cleaning and pattern development. Measurement of cleanliness under these processing conditions is very critical.
Cleaning, rinsing, and subsequent drying processes are often performed and controlled almost “blindly” and based on trial and error or past experience. The way these processes are monitored and controlled presently is based on ex-situ testing of wafer, chips, or structures. Within the process tool, fixed recipes are provided by tools and process suppliers. Run-by-run adjustments or control are based on external and delayed information on product performance or product yields. The sensors that are currently available are used in the fabs to monitor the conditions of fluid inside the process vessels and tanks, but far away from the inside of micro features (that is what needs to be monitored; it is also the bottleneck of cleaning and drying). The present monitoring techniques and devices do not provide realistic and accurate information on the cleanliness and condition of micro features.
Industry currently works around this problem while waiting for a solution; the process condition and cleaning and drying are often set with very large factors of safety (over-cleaning and over-rinsing). Large quantities of water and other chemicals are used (much more than what is really needed). This results in wasted chemicals and water, increased process time, lowered throughput, increased cost, and it causes reliability issues because of lack of process control.